Is this feasable and accurate enough ?

[Kevdan]

Hi All,

So I saw this.

Rotary Angle Encoder and Remote Display, with a 6mm diameter shaft.

If the mount was polar alinged properly before hand using a polarscope and wondered if I mad a plug to fit into the back of the polarscope holder so that the polarscope is removed once aligned, then using the removeable polarscope holder that is now redundent as EQ3 polar scope come with new "mounts" with it measuring angular movement 0-360' + or - 0.1 degree then would it be accurate enough to use, I know that RA of hours mins seconds would have to be converted to degrees but thats just simple maths for example M1 the Crab Nebula has a RA of 5h 34m 31.97s which would convert to 23.63344' rounded up to 23.6'

So would it work ? I know its not supre accurate like a goto but it would be a lot more accurate than the setting circles.

Kev.

just to Add this would give Digital readouts with 3600 positions (360' x 10x0.1 increments) where as the settign circles are only 144 positions (24h x 6x10min increments)

[Ad Astra]

Most digital setting circles are at least 1000 position encoders (0.36 degrees per increment).

Dec is easy to convert! For example:

25 d, 32m 21 s

(21s / 60) + 32m = 32.35m, Then

(32.35m / 60) + 25 deg = 25.522 deg

You encoder would allow you to get to +/- 0.36 degrees, so you could get to 25.56 deg (the 71st encoder position). You can only go up or down by 1/3 of a degree, but that should be enough to get you in the field of view for most any planet or DSO with a low power eyepiece.

Example For RA where 1h = 15 deg:

12h, 16m, 32s

(32s / 60) + 16m = 16.533m, then

(16.533m / 60) + 12h = 12.275h, then

12.275h x 15 = 184.133 degrees

Here your encoder would allow you to get to 184.32 deg (12h, 17m, 16.8s) - the 512th encoder position. As with Declination, plenty close enough to get you within the field of a low power EP.

Hope that helps some,

Dan

[Kevdan]

You encoder would allow you to get to +/- 0.36 degrees

But this encoder is +/- 0.1' so therefore much more accurate and I'm presuming a lot cheaper than made for Astronomy Digital scales.

It would be nice to see how it deals with the small amount of backlash in the gears as well.

I may just give it a go.

Kev.

[Astro Imp]

Hi Kev,

Interesting project for you.

If you decide to go ahead don't forget to let us all know the outcome.

Good luck.

[Kevdan]

Hardest thing is to make the bracket to hold it to the scope.

[Ad Astra]

Sorry Kev, I read that as +/- 1-degree. It is really 0.1 arc-minute? Wow. Most encoders I see for general engineering purposes are multiples of 1000 (or 1024 for computerized use). But in any case, the math is the same - just adjust for the interval. As long as you get it mounted properly it will work.

From other DIY setups I've seen, the mount is critical. Slop or wobble in the mounting kills the accuracy (and repeatability) of the mechanism.

Post a photo when you finish and let us know how it goes.

Dan

But this encoder is +/- 0.1' so therefore much more accurate and I'm presuming a lot cheaper than made for Astronomy Digital scales.

It would be nice to see how it deals with the small amount of backlash in the gears as well.

I may just give it a go.

Kev.

[Bazzaar]

Thats a really good idea Kev!

I'd just echo what Dan says, fabricating the mount for it that has less wobble or flex than the .1 deg that the encoder can measure to will be a challenge, but go for it! And keep us updated, interesting project.

Regards

Barry

[Kevdan]

I cant do anything for a few weeks as Im off to Turkey for a fortnight on 9th june but when I get back I'll have a go, As I was a toolmaker/toolsetter using machine tools I still know a lot of people that could make something up, One thing I need to do is to make a mount that can be installed and took out using NO TOOLS just simple thumb screws or clips (thumbscrew would be better) due to having to polar aling the scope with a polar scope then having to take out the polar scope to fit the old polarscope holder with a bush to suit the 6mm drive for the encoder.

I'll keep you all posted. But I'm on a mission now and if it is successfull, I will need volunteers to copy and try what I do to test.

Kev